Antennas are designed to transmit and receive electro-magnetic waves. Antennas for various purposes are continuously being further researched and developed.
A phased array antenna is an antenna with a directive radiation pattern which can be controlled by controlling individual radiator elements or groups of radiator elements in the antenna. In general, the steering direction of the radiation pattern is determined by control of the phases of the signal to or from the radiator elements. The phase control is achieved by phase shifters which should have low transmission loss.
One requirement for a phased array antenna is the provision of sufficient co-polarized gain over a wide range of scanning angles with sufficient beam sharpness and low side and grating lobe radiation. In this case wide angle scanning refers to from about 5° above the horizon up to 90° with the full 360° azimuth coverage. Such an antenna is primarily used in the aircraft industry where both profile height, surface area occupied and weight are important.
To achieve wide angle scanning without the appearance of grating lobes a very compact array element spacing is required. This in turn requires a compact, yet efficient, radiating element. Furthermore, to ensure low side lobe radiation the array antenna aperture should be tapered, i.e. the individual radiator elements occupying different positions within the array are excited with different magnitudes corresponding to the requited taper. This is implement by a array feed network.
The ability of a phased array antenna to provide the necessary wide angle scanning radiation is further a function of the ability of the individual radiating elements embedded within the array to radiate in the required direction. This is generally a problem when scanning just above the horizon as the individual radiators themselves within the array environment do not have a sufficiently wide radiation beamwidth to provide adequate gain in these directions.
A conventional phased array antenna's directivity can be determined by measuring the projected aperture of the antenna in a given direction. As the array is scanned to lower elevation angles the projected aperture becomes less. To achieve wide angle scanning the projected aperture in the low elevation regions is an important consideration and often requires that the antenna be much larger than desired.
Generally a close radiator spacing of radiating elements exuding high levels of low elevation gain results in high levels of mutual coupling between the elements. This mutual coupling, if not properly accounted for can often negatively influence the gain performance of the antenna.
Radiators with high levels of low elevation radiation are generally higher, such as various types of helices and dipoles that stand upright. These antenna elements have the advantage of occupying a small planar surface area facilitating a close radiator spacing. However these antennas are unsuited to a market where a lower profile height is desirable for both aerodynamic and aesthetic considerations.
It is an object of the invention to suggest an antenna, which will assist in overcoming these problems.